Methane –
Sources and Sinks
Leif Backman
HENVI Seminar
February 19, 2009
Background
• Atmospheric methane
• Sources & Sinks
• Concentration variations & trends
Objective & methods
• Objective & Goals
• Research plan
• Methods
• Tools
Previous research, cooperation & progress
Open questions & recent findings
• Methane growth rates
• Partitioning between sources
• Lifetime, BVOC & OH
• Soil freezing
Background
Atmospheric methane
Sources & Sinks
Concentration variations &
trends
Atmospheric methane
•
The natural range is 320 to
790 ppb, determined from
ice cores of the last 650000
years
•
CH4 concentrations have
more than doubled since
preindustrial times
700 ppb -> 1780 ppb
•
Sources identified, but
partitioning poorly known
•
More than half from
anthropogenic sources
•
Main sink, tropospheric OH
IPCC, 2007
•
Change in radiative
forcing 1750 -> 2005
•
Methane (CH4) is the 2nd
most important
anthropogenic
greenhouse gas after
CO2
•
CH4 is a ca. 20 times
more potent greenhouse
gas than CO2 (per mass)
IPCC, 2007
Methane sources
•
•
Biogenic CH4 sources (> 70% of the global total)
• wetlands
• rice agriculture
• livestock
• landfills
• biomass burning
• forests
• oceans
• termites
Non-biogenic CH4 sources
• emissions from fossil fuel mining and burning
• natural gas, petroleum and coal
• waste treatment
• geological sources
• fossil CH4 from natural gas seepage
• geothermal/volcanic CH4
IPCC, 2007
Methane sources
•
•
•
Natural sources
• Wetlands
• Termites
• Oceans
• Hydrates
• Geological sources
• Wild animals
• Wildfires
Anthropogenic sources
• Energy & industry (fossil fuels)
• Landfills & waste
• Ruminants
• Rice agriculture
• Biomass burning
Total sources
145–260 Tg/a
100–231
20–29
4–15
4–5
4–14
15
2–5
264–428 Tg/a
74–106
35–69
76–92
31–112
14–88
503–610 Tg/a
IPCC, 2007
Methane sinks
•
Sinks
• Tropospheric OH
•
492–577 Tg/a
428–507
• Stratosphere (OH, Cl, O1D, hv)
30–45
• Soils
26–43
Methane chemistry
• Decreases the amount of tropospheric OH
• Precursor for ozone production
• Stratosphere
• Source of water vapor
• Terminates ozone loss cycles by converting Cl to HCl
• Affects ozone through OH
Greenhouse gas concentrations
NOAA global flask sampling network, http://www.esrl.noaa.gov/gmd/ccgg/
•
•
•
•
•
Consistently higher CH4
emissions in the NH
CH4 emissions from
wetlands mostly during
warm seasons
OH concentration
increases with sunlight
=> The maximum of
atmospheric CH4 in the
NH reached in late
autumn or even in winter
Seasonal changes in
CH4 emissions and
photochemical
oxidation, causes the
seasonal cycle and a
shift in phase between
NH and SH
Objective & methods
Objective & Goals
Research plan
Methods
Tools
Objectives and goals
• The main objective is to improve the understanding of
how sources and sinks influence the atmospheric
abundance and growth rate of CH4, and the
subsequent effect on the climate
• The principal tool for these studies will the ECHAM5HAMMOZ, and the practical goal is to improve the
parameterization of CH4 sources
• Long-term goals
• Improved Earth system models
• To develop a coupled biosphere-CCM including a
realistic description of the response of CH4 emissions
from wetlands for different hydrological conditions
Research plan
I)
II)
Implementation of the chemistry climate model (ECHAM5HAMMOZ) to the high performance computing facilities at FMI
Methane lifetime studies
•
III)
IV)
V)
VI)
CH4, OH, CO, BVOC …
Review of in situ data
Review of remote sensing data
•
soil melting/freezing
•
land use
•
snow cover
•
trace gas data (CH4, CO, CO2)
Parameterization of methane source emissions
Effect of meteorology on global and local methane growth rates
(comparison to observations)
•
nudged model runs (ECMWF)
VII) Inverse modelling
VIII) Coupled biosphere-chemistry-climate model
ECHAM5-HAMMOZ CCM
•
Chemistry & Aerosol coupled GCM (Pozzoli et al.,
2008)
Methane lifetime
• Reaction with tropospheric OH (85-90%)
• OH formed when ozone is photo-dissociated:
• O3 + hv -> O1D + O2
• O1D + H2O -> OH + OH
• OH concentrations affected by CH4, CO and BVOCs
• Increase in methane leads to positive feedback
• Variations in UV (stratospheric ozone, aerosols)
affects OH
• Urban areas, NOx -> O3 -> OH production
• The distribution of OH can be estimated using
compound that have known sources and sinks e.g.
methyl chloroform (CH3CCl3)
Methane lifetime
• Growth rate declined
since early 1990s
=>around zero during the
last decade with large
interannual variations
• Changes in main sink, OH,
can be due to
• Changes in BVOC
emissions (Pinatubo)
• CO emissions (e.g.
biomass burning)
• Changes in NH wetland
and anthropogenic
methane emissions
Satellite data of CH4, CO and CO2
• SCIAMACHY/Envisat – ESA
• data available for 2003–2005
• GOSAT – JAXA
• first light Feb 2009
• OCO – NASA
• to be launched in Feb 2009
• Global coverage
• Column mixing ratio
• Model validation
• Inverse modeling?
Previous research,
cooperation & progress
Previous experience
• Global stratospheric chemistry modeling
• Process studies and long-term development of ozone
• PSC and aerosol processing
• Ozone loss rates
• Chemical and Dynamical effects on long-term ozone
changes
• Past/future ozone trends
• Ozone recovery
• Chemistry-climate coupling
• FinROSE-ctm (ECMWF-, CCM-data)
• HAMMONIA-CCM
Multidisciplinary cooperation
•
Measurements
• Local (+ network data)
• In situ data (FMI, UH)
• Concentrations
• Fluxes
• Column data (FMI)
• FTIR
• Global
• Satellite data (FMI)
• CH4, CO, CO2
• Land use
• Soil melting/freezing, snow cover
•
•
Atmospheric modelling (FJ-ICG, COSMOS, FMI, UH)
• Inverse modelling (LUT, FMI)
Biosphere modelling (UH, FMI)
Progress
• ECHAM5-HAMMOZ implemented to FMI HPC facilities
Open questions &
recent finding
Methane growth rates
Partitioning between sources
Lifetime, BVOC & OH
Soil freezing
Methane and BVOCs
•
•
•
•
•
Evaluation of the interhemispheric gradient in atmospheric CH4 at times
in the past is possible because of the existence of ice cores in the high
latitudes of both hemispheres (past 21 000 yrs).
These interhemispheric gradients may be used to imply temporal
changes in the geographic distribution of CH4 sources and sinks.
In contrast to CH4, which is relatively well mixed in the atmosphere, the
short lifetimes of BVOCs mean that their effect on OH is mostly local.
Differences between poles mainly due to changes in OH mainly due to
changes in BVOCs
Kaplan et al., Role of methane and biogenic volatile organic compound
sources in late glacial and Holocene fluctuations of atmospheric
methane concentrations, Global Biogeochem. Cycles., 2006.
BVOCs and OH
•
•
•
•
Previously it was thought that, in unpolluted air,
BVOCs deplete OH and reduce the atmospheric
oxidation capacity
Aircraft measurements of atmospheric trace gases
performed over the pristine Amazon forest reveal
unexpectedly high OH concentrations
Natural VOC oxidation, notably of isoprene,
recycles OH efficiently in low-NOx air through
reactions of organic peroxy radicals ?
Lelieveld et al., Atmospheric oxidation capacity
sustained by a tropical forest. Nature, 2008.
Methane emissions and soil freezing
•
•
•
The emissions fall to a low steady level after the growing season
but then increase significantly during the freeze-in period
The integral of emissions during the freeze-in period is
approximately equal to the amount of methane emitted during
the entire summer season
CTM simulations of global atmospheric methane concentrations
indicate that the observed early winter emission burst improves
the agreement between the simulated seasonal cycle and
atmospheric data from latitudes north of 60°N
•
In addition spring burst from trapped methane during the winter
have been observed earlier
•
Mastepanov et al., Large tundra methane burst during onset of
freezing, Nature, 2008.
Methane emission during soil freezing
Mastepanov et al., Large tundra methane burst during onset of freezing,
Nature, 2008.
Summary
• The main objective is to improve the understanding of
how sources and sinks influence the atmospheric
abundance and growth rate of CH4, and the
subsequent effect on the climate
• Several ‘open questions’ regarding methane
• Many possibilities for cooperation in the Kumpula
campus
• in situ measurements and remote sensing data
• biosphere modeling
• tropospheric CCM modelling
• inverse modeling